Impulsive loading of sandwich panels with cellular cores

Metallic sandwich panels with a cellular core such as honeycomb or metal foam have the capability of dissipating considerable energy by large plastic deformation under quasi-static or dynamic loading. The cellular microstructures offer the ability to undergo large plastic deformation at nearly constant stress, and thus can absorb a large amount of kinetic energy before collapsing to a more stable configuration or fracture. To date, research on the performance of sandwich structures has been centred on their behaviours under quasi-static loading and impact at a wide range of velocities, but work on their blast loading response is still very limited. A series of analytical and computational models have been developed by previous researchers to predict the dynamic response of a sandwich beam or circular sandwich panel. However, no systematic studies have been reported on square sandwich panels under blast loading. In this research, experimental, computational and analytical investigations were conducted on a number of peripherally clamped square metallic sandwich panels with either honeycomb or aluminium foam cores. The experimental program was designed to investigate the effect of various panel configurations on the structural response. Two types of experimental result were obtained: (1) deformation/failure modes of specimen observed in the tests; and (2) quantitative results from a ballistic pendulum with corresponding sensors. Based on the experiments, corresponding finite element simulations have been undertaken using commercial LS-DYNA software. In the simulation work, the explosive loading process and response of the sandwich panels were investigated. A parametric study was carried out to examine the plastic deformation mechanism of the face-sheet, influence of boundary conditions, as well as the plastic energy dissipating performance of the components of the sandwich panels. Two analytical models have been developed in this study. The first model is a design-oriented approximate solution, which is excellent for predicting maximum permanent deflections, but gives no predictions of displacement-time histories. The analysis is based on an energy balance with assumed displacement fields, where either small deflection or large deflection theory is considered, according to the extent of panel deformation. Using the proposed analytical model, an optimal design has been conducted for square sandwich panels of a given mass per unit area. The second analytical model has the ability of capturing the dynamic structural response. A new yield criterion was developed for a sandwich cross-section with different core strengths. By adopting an energy dissipation rate balance approach with the newly developed yield surface, upper and lower bounds of the maximum permanent deflections and response time were obtained. Finally, comparative studies have been conducted for the analytical solutions of monolithic plates, sandwich beams, circular and square sandwich panels.